Single-photon source with sub-MHz linewidth for cesium-based quantum information processing

A single-photon source with narrow bandwidth, high purity, and large brightness can efficiently interact with material qubits strongly coupled to an optical microcavity for quantum information processing. Here, we experimentally demonstrate a degenerate doubly resonant single-photon source at 852 nm by the cavity-enhanced spontaneous parametric down-conversion process with a 100% duty cycle of generation. The single photon source possesses both high purity with a second-order correlation g h (2) (0) = 0.021 and narrow linewidth with Δ ν sp = (800 ± 13) kHz. The single-photon source is compatible with the cesium atom D2 line and can be used for cesium-based quantum information processing.